1. Field of the Invention
The present invention generally relates to a semiconductor device and a method of forming the same. More particularly, the present invention relates to a thin film transistor and a method of forming the same.
2. Description of Related Art
A thin film transistor (TFT) typically includes a gate, a gate insulating layer, a channel layer, a source electrode and a drain electrode, and is usually used as a switching device in displays such as liquid crystal displays (LCD). Usually, the TFT is formed by sequentially forming a gate, a gate insulating layer, an α-Si channel layer, a source electrode and a drain electrode on a substrate. The gate is constituted of a single metal layer of aluminum (Al), chromium (Cr), tungsten (W), tantalum (Ta) or titanium (Ti), or constituted of multiple metal layers.
However, when a single-layered of the above-mentioned metal is used to form the gate, the surface of the layer is easily eroded and easily reacts with oxygen in the atmosphere to form a metal oxide that cannot be effectively etched in the subsequent etching process. On the other hand, when the gate is constituted of multiple metal layers, such as molybdenum (Mo)/Al/Mo, to prevent oxidation and erosion, the process for forming multiple metal layers is surely more complex because more than one sputtering targets and deposition chambers are required. Moreover, the above problems also occur in the process for forming the source electrode and the drain electrode.